JP3564800B2 - Distance measuring device - Google Patents

Description

[0001]
[Industrial applications]
The present invention detects a reflected wave from a reflecting object by intermittently radiating a pulsed transmission wave, and detects a distance to the reflecting object based on a time difference between a time when the transmitted wave is emitted and a time when the reflected wave is detected. To a distance measuring device that calculates
[0002]
[Prior art]
Conventionally, for example, intermittently radiating a pulsed transmission wave such as a light wave or a millimeter wave to detect a reflected wave reflected by a reflecting object, and radiating the transmitted wave and detecting the reflected wave JP-A-59-142488, JP-A-60-201276, JP-A-62-15480, and the like are known as distance measuring devices for calculating the distance to a reflecting object based on the time difference between the two.
[0003]
Japanese Patent Application Laid-Open No. Sho 59-142488 discloses a technique in which the receiving sensitivity of a reflected light signal is reduced to a predetermined level at the time of transmitting an optical signal and is increased with time thereafter, and a so-called STC (Sensitivity Time Control) is used. It has been adopted. When the vehicle travels in a fog or snowfall situation, light scattered and reflected by fog and snow particles is received. Although the reflectivity of fog and the like is considerably smaller than that of a vehicle body or the like, since the light is reflected from a short distance, the received light intensity itself is large (the intensity of the reflected light is inversely proportional to the fourth power of the distance). Therefore, if the distance is calculated as it is, the distance is calculated based on the reflected light from the fog. To prevent this, the receiving sensitivity is reduced at a short distance.
[0004]
Japanese Patent Application Laid-Open No. 60-201276 discloses that a light receiving intensity range of reflected light with respect to a distance to a particle floating in the air such as fog when light is output is stored in advance, and a light receiving signal level is determined by the light receiving signal level. When the intensity is within the range, the distance is not output. Specifically, if the received light intensity is less than 20P (P is the shortest detection limit intensity) and the distance L is less than 20m, it is regarded as a reflection signal from fog.
[0005]
Japanese Patent Application Laid-Open No. Sho 62-15480 discloses a fog detection device for a vehicle. When the traveling speed of the vehicle indicates a predetermined value or more and the distance data continuously outputs a state of a predetermined value for a predetermined time or more, the fog is detected. Is determined to have occurred. This is based on the following viewpoints. That is, for example, when the preceding vehicle is traveling at a predetermined speed or higher, or when the obstacle is a stationary object (including a stationary vehicle), the distance data to the target object changes immediately. Even when the vehicle is traveling at a speed similar to that of the vehicle equipped with the present apparatus, the distance between the two vehicles is constantly changing, and it is considered that the distance between the vehicles does not show a constant value for a predetermined time or more. On the other hand, when fog is generated in the detection area, the distance data is considered to be constant regardless of the traveling speed of the vehicle equipped with the present device.
[0006]
[Problems to be solved by the invention]
However, the above-described related art has the following problems.
{Circle around (1)} The low-reflection object cannot be distinguished from fog or the like, and the low-reflection object at a short distance is overlooked.
[0007]
{Circle around (2)} When fog is detected, a target object whose distance should be measured is overlooked.
JP-A-59-142488 and JP-A-60-201276 mentioned above focus on characteristics such as fog such as "occurring at a short distance" and "small reflectance" to improve the reception sensitivity of a reflected light signal. When transmitting an optical signal, the sensitivity is set to a low level of a predetermined level, and thereafter, the sensitivity is increased over time. When the light receiving signal level is within a predetermined light receiving intensity range, the distance is not output. Therefore, when the low-reflection object is at a short distance, it cannot be distinguished from fog, and is likely to be overlooked.
[0008]
In the case of a reflector or a white body of a preceding vehicle, the reflectance is high, but for example, a person wearing dark clothes, a dirty car, a dark car, or a lower portion of a truck bed becomes a low reflection object. A supplementary note is that the lower part of the truck bed is a low reflection object. Transmitted waves are radiated so as to be reflected by the reflectors and bodies of ordinary passenger cars, so in the case of trucks with a high vehicle height, they are reflected near the lower part of the cargo bed, and may act as low-reflection objects. .
[0009]
Further, in the fog detecting device for a vehicle disclosed in Japanese Patent Application Laid-Open No. Sho 62-15480, it is further considered that the distance data is constant irrespective of the traveling speed of the vehicle equipped with the device. It is possible to distinguish occurrences. However, since basically only one target can be detected, if fog is detected, the target farther away than that, which should be measured, is overlooked.
[0010]
Therefore, the present invention can detect a reflected wave from a plurality of reflecting objects with respect to the same transmission wave, and can measure a distance when a signal from a target exists even when a reflected wave from snow, fog, etc. is detected. It is an object of the present invention to provide a simple distance measuring device.
[0011]
[Means for Solving the Problems]
The invention according to claim 1 made to achieve the above object,
A time difference measuring unit that intermittently emits a pulsed transmission wave to detect a reflected wave from a reflecting object, and measures a time difference between a time when the transmitted wave is emitted and a time when the reflected wave is detected; A distance calculating means for calculating a distance to the reflective object based on the time difference measured by the measuring means, wherein the time difference measuring means comprises: In addition to detecting reflected waves, it is possible to measure the time difference corresponding to each reflected wave, and in the case of weather conditions such as snow, fog, rain, etc., particles floating in the air scatter and reflect the transmitted wave Storage means for storing in advance the range of the time difference corresponding to the reflected wave generated by the Calculation Means for calculating a distance to the reflecting object based on the time difference measured by the time difference measuring means and the time difference range data in the case of scattered reflection stored in the storage means. Device.
[0012]
The invention according to claim 2 is
2. The distance measuring device according to claim 1, wherein the distance measuring device further includes a travel determination unit that determines whether the vehicle is traveling. Calculation The means, in addition to the time difference measured by the time difference measuring means and the time difference range data in the case of scattered reflection stored in the storage means, By travel judgment means A distance measuring device for calculating a distance to the reflective object based on a determination result as to whether or not the vehicle is running.
[0013]
The invention described in claim 3 is:
3. The distance measuring device according to claim 2, wherein the vehicle is traveling, and a time difference measured by the time difference measuring means is continuously greater than a predetermined number of times within a time difference range in the case of the scattered reflection stored in the storage means. If it enters at, it is determined that the time difference is due to scattered reflection from fog etc. The distance calculating means is: A distance measuring device for calculating a distance to the reflective object based on other time difference data.
[0014]
Further, the invention described in claim 4 is:
2. The distance measuring device according to claim 1, wherein the time difference measuring means scans and radiates the transmission wave in a predetermined angle range in a vehicle width direction, and detects the time difference corresponding to a scan angle. When a plurality of reflected waves are detected for one transmission wave and the time difference corresponding to each reflected wave is measured by the time difference measuring means, the shortest time difference data among the plurality of time difference data is configured. However, it is provided with a judgment means for judging whether or not substantially the same at many scan angles, and when the judgment means judges that there is substantially the same shortest time difference data at many scan angles, distance Calculation The distance measuring device is characterized in that the means calculates the distance to the reflecting object based on the next time difference data next to the shortest time difference data among the plurality of time difference data.
[0015]
On the other hand, the invention described in claim 5 is
2. The distance measuring device according to claim 1, wherein the time difference measuring means scans and radiates the transmission wave in a predetermined angle range in a vehicle width direction, and detects the time difference corresponding to a scan angle. When a plurality of reflected waves are detected for one transmission wave and the time difference corresponding to each reflected wave is measured by the time difference measuring means, the shortest time difference data among the plurality of time difference data is configured. Comprises, at the many scan angles, determination means for determining whether or not the time difference is within the range of the case of the scattered reflection stored in the storage means, and the determination means makes the shortest at many scan angles The time difference data is within the time difference range in the case of the scattering reflection. Was determined to be If the above distance Calculation The distance measuring device is characterized in that the means calculates the distance to the reflecting object based on the next time difference data next to the shortest time difference data among the plurality of time difference data.
[0016]
[Action]
In the invention having the above-described configuration, the time difference measurement unit radiates the pulsed transmission wave intermittently, detects a plurality of reflected waves for one radiated transmission wave, and calculates a time difference corresponding to each reflected wave. It can be measured. Therefore, for example, even if there is a fog on the near side and there is a target that you want to measure the distance on the other side, the time difference due to the reflected wave from the fog on the near side is measured, and the original distance in the distance is measured. The time difference due to the reflected wave from the target to be measured can be measured without overlooking. Then, the distance calculating means calculates the distance to the reflecting object based on the time difference measured by the time difference measuring means. However, simply measuring a plurality of time lag data cannot determine whether the data is due to fog or the like or the originally measured target. Therefore, the present invention has a feature in the distance calculation.
[0017]
That is, the storage means stores in advance the range of the time difference corresponding to the reflected wave generated by scattering and reflecting the transmission wave by the particles floating in the air in the case of weather conditions such as snow, fog, and rain, The above distance Calculation The means calculates the distance to the reflecting object based on the time difference measured by the time difference measuring means and the time difference range data for the scattered reflection stored in the storage means.
[0018]
Therefore, for example, when the vehicle is traveling in a mist or snowfall state, and there is a preceding vehicle or an obstacle in front, the time difference measuring unit is scattered by fog or snow particles. Two time differences are measured: a time difference corresponding to a reflected wave generated by reflection and a time difference corresponding to a reflected wave generated by being reflected by a preceding vehicle existing ahead.
[0019]
Reflected waves generated by being scattered and reflected by fog and snow particles frequently occur at short distances. Therefore, when two time differences are measured as described above, the shorter time difference is due to the scattered reflection of fog or snow, and the longer time difference is due to the reflected wave from the preceding vehicle or the like. As described above, by detecting reflected waves from a plurality of reflecting objects with respect to the same radiation wave, even when a reflected wave from fog or the like is detected, distance measurement can be performed when a signal from a target exists.
[0020]
In addition, as described in claim 2, whether or not the vehicle is running is determined by the travel determining means, and the distance is determined. Calculation Distance in means Calculation In, when the determination result is taken into account, more accurate distance measurement to the target can be performed. For example, when a low-reflection object is at a short distance, it is the same as fog or the like having the characteristic of “occurring at a short distance” and “small reflectance”, It is indistinguishable whether the light is scattered and reflected light, but it can be distinguished as follows by taking into account that the vehicle is traveling.
[0021]
For example, when the preceding vehicle is traveling at a speed higher than the traveling speed of the own vehicle or when the obstacle is immovable (including a stopped vehicle), the time difference data to the object changes immediately, and Even when the preceding vehicle is running at the same speed as the own vehicle, it is rare that the exact same speed continues, and the distance between both vehicles is constantly changing, and it is constant for a predetermined time or more. It is thought that there is no.
[0022]
On the other hand, when fog or the like is generated in the detection area, the distance data due to the fog or the like is considered to be constant at a close distance, regardless of the traveling speed of the own vehicle, and thus it is determined to be fog or the like. be able to. Therefore, for example, when the vehicle is running and the measured time difference falls within the range of the time difference in the case of the scattered reflection for a predetermined number of times or more, the time difference is caused by scattering from fog or the like. If it is determined that the reflection is due to reflection and the distance to the reflecting object is calculated based on the other time difference data, necessary distance data can be obtained.
[0023]
Further, in a case where the time difference measuring means scans and radiates the transmission wave in a predetermined angle range in the vehicle width direction and the time difference can be detected according to the scan angle, the following can be performed. . In other words, when a plurality of reflected waves are detected for one transmission wave and the time difference corresponding to each reflected wave is measured, the determining unit determines that the shortest time difference data among the plurality of time difference data is the number of scans. It is determined whether or not the angles are substantially the same, and if there is almost the same shortest time difference data at many scan angles, the distance is determined. Calculation The means calculates the distance to the reflecting object based on the longest time difference data next to the shortest time difference data among the plurality of time difference data.
[0024]
In other words, in the case of the reflected wave of the preceding vehicle, substantially the same time difference data is obtained only for a part of the scan angles, and it is considered that almost the same time difference data is hardly obtained at many scan angles. It is conceivable that fog exists over almost the entire scan area due to its nature. Therefore, if there is almost the same shortest time difference data at many scan angles, it is considered to be due to fog or the like and is not adopted, and the distance to the reflecting object is determined based on the next longest time difference data after the shortest time difference data. By performing the calculation, it is possible to accurately distinguish only the target object whose distance is to be measured and measure the distance.
[0025]
Note that it is determined whether the time difference data is substantially the same at many scan angles, but this takes into account detection errors and the like. When performing predetermined data processing based on raw data detected by a sensor or the like, it is general, and thus a detailed description will not be given.
[0026]
On the other hand, the distance measuring device according to the fifth aspect scans and radiates a transmission wave in a predetermined angle range in the vehicle width direction in a manner similar to the fourth aspect, and is capable of detecting a time difference corresponding to the scan angle. However, when a plurality of reflected waves are detected with respect to one transmission wave and the time difference corresponding to each reflected wave is measured, the determining means according to claim 5 makes the following determination. That is, it is determined whether or not the shortest time difference data among the plurality of time difference data is within the time difference range for the scattered reflection stored in the storage means at many scan angles. Then, according to the determination means, it is within the time difference range in the case of scattered reflection at many scan angles. Was determined to be If the distance Calculation The means calculates the distance to the reflection object based on the longest time difference data next to the shortest time difference data among the plurality of time difference data.
[0027]
Such a distance measurement takes into account the following points. The time difference data corresponding to the reflected wave generated by scattering and reflection by particles floating in the air under weather conditions such as snow, fog, rain, etc. is mainly due to the so-called light curtain phenomenon by these floating particles In principle, substantially the same time difference data should be obtained. However, actually, the density of the suspended particles may be different within a predetermined angle range where the transmission wave is scanned and emitted. In particular, in the case of fog, it is sufficiently possible that local fog is generated. Such a difference in the density of the suspended particles is reflected in a difference in the transmittance with respect to the transmission wave.
[0028]
If the transmittance is small, the detection signal level of the reflected wave will increase as a result, and its peak value will also increase. Conversely, if the transmittance is large, the detection signal level of the reflected wave becomes small, and the peak value becomes small. FIG. 8A shows, as an example of a schematic image of the detection signal, three detection signal curves L1 to L3 when the transmittance is different. As shown in FIG. 8A, the detection signal is made valid at the time when the detection limit is exceeded, so that the three detection signal curves L1 to L3 have different times when the detection limit is exceeded. Assuming that the times at which the curves L1, L2, L3 exceed the detection limit are respectively t1, t2, t3, a distance corresponding to the time difference occurs as a measurement error. For example, when the time difference between the time t1 and the time t3 is converted into a distance, the distance may be 5 to 6 m. That is, although snow, fog, and the like exist, they may not be detected as substantially the same time difference data due to partial differences in their densities (density of suspended particles).
[0029]
Therefore, even if different time difference data is measured, if the distance measurement device is within the time difference range in the case of scattered reflection at many scan angles, the distance measuring device of the present invention still has the possibility of snow or fog. The target object for which the distance should be measured by calculating the distance to the reflecting object based on the longest time difference data next to the shortest time difference data without judging that there is an existing time difference data Only the distance can be accurately distinguished and the distance can be measured.
[0030]
In the distance measuring device according to the fifth aspect, as shown in FIG. 8A, the times t1, t2, and t3 at which the three detection signal curves L1 to L3 exceed the detection limit are different, and the time difference between these times is different. The description has been made on the assumption that the distance corresponding to is a size that cannot be ignored (for example, a distance such as 5.6 m). However, if the component for detecting the reflected wave and converting it into a signal has a function of making the rising of the detection signal steep, as shown in FIG. The time difference at each of the times t1, t2, and t3 at which the signal curves L1 to L3 exceed the detection limit is shortened, and it is possible to consider it as substantially the same time difference data. If the generated time difference can be made smaller than the time resolution of the time difference measuring means, there is no error due to the difference in transmittance in principle.
[0031]
As described above, when the component for detecting the reflected wave and converting it into a signal is configured such that the time difference due to the difference in transmittance is short and can be regarded as substantially the same time difference data, or no error occurs. As shown in the above, if there is substantially the same shortest time difference data at many scan angles, it is considered that it is due to fog or the like, and it is not adopted. It is also possible to cope with a case where transmission densities are different due to different densities.
[0032]
In addition, if the distance data to the target obtained by the distance measuring device described above is used, various types of vehicles such as an obstacle warning and a collision prevention, or a control of following a preceding vehicle while maintaining a predetermined inter-vehicle distance can be used. This is preferable when running control is performed.
[0033]
【Example】
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram illustrating a distance measuring device 1 according to an embodiment. The distance measuring device 1 according to the present embodiment is mounted on an automobile and detects an obstacle (reflective object) in front of the vehicle.
[0034]
The distance measuring device 1 is configured as follows, with the transmission / reception unit 31 and the calculation unit 33 as main components. As shown in FIG. 1, the transmission / reception unit 31 includes a semiconductor laser diode (hereinafter simply referred to as a laser diode) 39 that emits a pulsed laser beam H via a scan mirror 35 and a light-emitting lens 37, and a failure (not shown). A light receiving element 43 that receives the laser beam H reflected by the object through the light receiving lens 41 and outputs a voltage corresponding to the intensity thereof.
[0035]
The laser diode 39 is connected to the calculation unit 33 via a drive circuit 45, and emits (emits) laser light H according to a drive signal from the calculation unit 33. A mirror 47 is provided on the scan mirror 35 so as to be swingable about a vertical axis. When a drive signal from the calculation unit 33 is input via a motor drive unit 49, the mirror 47 is driven by a motor (not shown). Swing by the driving force. Then, the laser beam H is swept in front of the vehicle at a predetermined angle in a horizontal plane.
[0036]
On the other hand, the output voltage of the light receiving element 43 is amplified to a predetermined level via a sensitivity time control (STC) circuit 51 and then input to a variable gain amplifier 53. The STC circuit 51 will be supplementarily described. Since the received signal strength is inversely proportional to the fourth power of the distance to the target, the STC circuit 51 is provided to compensate for a case where there is a high reflectance such as a reflector at a short distance and the received light intensity becomes extremely strong. ing.
[0037]
Further, the variable gain amplifier 53 is connected to the calculation unit 33 via the D / A converter 55, amplifies the input voltage according to the gain (gain) specified by the calculation unit 33, and outputs the input voltage to the comparator 57. The comparator 57 compares the output voltage V of the variable gain amplifier 53 with a predetermined voltage V0, and inputs a predetermined light receiving signal to the time measurement circuit 61 when V> V0.
[0038]
The time measurement circuit 61 also receives a drive signal output from the calculation unit 33 to the drive circuit 45, and sets the drive signal as a start pulse PA and the received light signal as a stop pulse PB, and the position between the two pulses PA and PB. The phase difference (that is, the input time difference) is encoded into a binary digital signal, and the value is input to the arithmetic unit 33. The time measuring circuit 61 can digitize the minute time, and can detect the time difference between each signal even if there are a plurality of light receiving signals with respect to the emitted laser light H1. .
[0039]
As the time measuring circuit 61, for example, a circuit using an odd number of ring oscillators in which an odd number of inverter gate delay circuits for inverting and outputting an input signal are connected in a ring shape and a pulse edge is circulated on the ring is conceivable. . The phase difference between the two pulses PA and PB (that is, the input time difference) is measured as follows. That is, when a start pulse PA is input, a pulse edge is circulated on the ring oscillator, and when a stop pulse PB is input, a pulse edge activated by the start pulse PA is applied to any inverter gate on the ring oscillator. The phase difference between the two pulses PA and PB is measured by detecting whether the pulse has reached the delay circuit.
[0040]
The time measurement circuit 61 also has a time resolution correction function for performing accurate time measurement. Here, digital operation correction by a completely digital circuit is performed by using a reference signal (for example, a crystal oscillation clock).
Conventionally, when a digital circuit is used for time measurement, the clock cycle is used as the resolution. However, the time measurement circuit 61 configured as described above uses the time (the above two pulses PA, PA) with a much smaller resolution than the clock circuit. The phase difference between the PBs can be quantified. Therefore, even if there are a plurality of light receiving signals with respect to the emitted laser beam H1 (that is, even if there are two or more stop pulses PB for one start pulse PA), the time difference between each signal is detected. You can do it. In the following description, this is expressed as "multi-wrap possible", and the data thus obtained is referred to as multi-wrap data.
[0041]
Returning to the description of the configuration in FIG. 1, the calculation unit 33 calculates the distance and direction to the obstacle based on the input time difference from the time measurement circuit 61 and the swing angle of the mirror 47 at that time. The output voltage V of the variable gain amplifier 53 is also input to the peak hold circuit 63, and the peak hold circuit 63 inputs the maximum value of the output voltage V to the calculation unit 33.
[0042]
The calculation unit 33 also receives a vehicle speed signal from a vehicle speed sensor (not shown). Next, the operation of the distance measuring device 1 configured as described above will be described. FIG. 2 is a flowchart showing the distance measurement processing executed by the arithmetic unit 33, and FIG. 3 is a time chart showing various signals at the time of distance measurement. FIG. 2A shows a case where there is one reflected signal, and FIG. Two cases are shown.
[0043]
First, as shown in FIG. 2, in step 100 (hereinafter, the step is simply referred to as S), a drive signal is output to the drive circuit 45 to cause the laser diode 39 to emit light (see FIGS. 3A and 3B). (1) to (3)). In the subsequent S105, the laser light H reflected on an obstacle (not shown) is received via the light receiving lens 41 in response to the light emission. Then, the received laser light H is converted into a voltage corresponding to the intensity by the light receiving element 43 and input to the time measuring circuit 61 via the STC circuit 51, the variable gain amplifier 53, and the comparator 57 (FIG. 3A). , (B) (4) and (5)). Then, even if there are a plurality of reflected signals with respect to the emitted laser beam H1, the time measuring circuit 61 detects a time difference between the respective signals (see (6) in FIG. 3B), and The data is input to the calculation unit 33 as lap distance data.
[0044]
The distance data input from the time measurement circuit 61 is stored in a RAM (not shown) of the calculation unit 33.
In this embodiment, when a drive signal from the calculation unit 33 is input to the scan mirror 35 via the motor drive unit 49, the mirror 47 swings and scans a predetermined area. As a result, the laser beam H is swept and irradiated at a predetermined angle in a horizontal plane in front of the vehicle. In S110, it is determined whether or not the scanning of all the predetermined areas is completed, and the processes of S100 and S105 are repeated until the scanning of all the areas is completed.
[0045]
When the scanning of all areas is completed, it is determined in S115 whether or not distance data exists. If there is no distance data, the process proceeds to S120, where only information that there is no target object is stored, and no distance data is output.
On the other hand, when the distance data exists (S115: YES), the process proceeds to S125, and the distance data is grouped according to the distance. This “grouping according to distance” will be described. As described above, in this embodiment, the laser beam is emitted by the scanning method in the present embodiment, and the laser diode 39 emits light every time the mirror 47 swings by a predetermined angle. 5 degrees). Therefore, the distance data is distinguished as the distance data corresponding to the laser beams H having different radiation directions. Even if the distance data is originally based on the reflected wave from the same object, it is processed as different data. Therefore, by grouping adjacent distance data, subsequent processing is simplified.
[0046]
Note that “proximity” may be defined by various conditions. However, taking into account the direction of emission of the laser light H, if there is very close distance data corresponding to adjacent emission directions, the group Is preferred. This is because, when the laser beam H is reflected back to the rear of the preceding vehicle, it is highly conceivable that a plurality of the laser beams H emitted at predetermined angles are reflected on the same vehicle. .
[0047]
In subsequent S130, it is determined whether or not multi-lap data exists. That is, it is determined whether there are a plurality of light reception signals for the emitted laser light H1 emission, that is, whether there are a plurality of distance data corresponding to the same laser light H emitted in the same emission direction. . Note that the shortest distance data when multi-lap data exists is called first data, and the next longest distance data is called second data.
[0048]
If multi-lap data is present (S130: YES), it is determined in S135 whether or not substantially the same short-distance data is present in many of the areas being scanned. In a snowy situation or a fog situation, it is likely that snow and fog particles are almost uniformly present in all areas to be scanned. For this reason, when snow and fog particles are almost uniformly present in all areas to be scanned, distance data generated by scattering and reflecting by the particles is present in many areas in all areas. Then, all the distance data are generated at a predetermined short distance.
[0049]
In the case of scanning, when scanning near the left and right ends compared to the center, the light receiving efficiency of the optical system may be reduced and fog may not be detected. Instead of "determining whether or not substantially the same short distance data exists in all areas", "determining whether or not substantially the same short distance data exists in many areas in all areas" I do it ".
[0050]
Note that it is determined whether the time difference data is substantially the same at many scan angles, but this takes into account detection errors and the like. Since it is common to perform predetermined data processing based on raw data detected by a sensor or the like, the word “substantially the same” will be used without particular description.
[0051]
Returning to FIG. 2, in S135, when the determination is affirmative, that is, when there is substantially the same short-distance data for many areas, it is determined in S140 that the state is snow / fog, and in the state of snow / fog. The information that there is is stored. Then, since the short distance data when there are substantially the same short distance data for many areas is the first data, the second data is output as the distance to the target in S145, and the process returns to S100.
[0052]
On the other hand, in the case of a negative determination in S135, that is, in a case where substantially the same short-distance data does not exist in many areas, that is, in a case where there is no substantially the same data or only a part has the substantially same data, Is not caused by fog or the like, the process proceeds to S155 to output the first data as the distance to the target, and then returns to S100.
[0053]
Subsequently, a description will be given of a case where a negative determination is made in S130, that is, a case where no multi-lap data exists. The absence of multi-lap data means that there is only one distance data. In this case, it is first determined in S150 whether the vehicle is traveling. This is determined by a signal from the vehicle speed sensor.
[0054]
If the vehicle is not running (S150: NO), that is, if the vehicle is stopped, the process proceeds to S155, outputs first data, and returns to S100. In this case, since there is only one distance data, all the distance data are the first data. The first data may be data based on fog or the like, and may be a vehicle instead of fog. However, since the own vehicle is in a stopped state, there is no problem without rear-end collision. Therefore, the first data is output in S155 because it may or may not be fog.
[0055]
On the other hand, when the vehicle is running (S150: YES), it is important whether the first data is due to fog or the like or another target, unlike during stopping. This is because erroneously recognizing that distance data due to fog or the like is due to a target or vice versa is that distance data due to a target is due to fog, for example, by using the distance data as an obstacle warning or the like. , The alarm effect is reduced. For example, if an alarm is always issued even though it is actually fog, the alarm effect in the scene where it is originally needed will be greatly diminished.
[0056]
Therefore, first, in S160, data of a distance range generated by reflected light scattered by particles such as fog and snow (hereinafter, referred to as “scattered light data”) is compared with the first data. The scattered light data has a value of, for example, 8 m or less, which is based on the fact that scattered light from snow, fog, and rain (water droplets) often occurs at a very short distance.
[0057]
FIG. 5 is an example of a measurement result of snow, and shows a relationship between a distance at which snow is detected and an occurrence ratio thereof. The difference in the amount of snowfall, that is, the difference in the density of the snow particles causes the transmittance of the laser beam to be different. FIG. 5 shows the results in three cases. The measurement result when the transmittance is relatively small is indicated by (■), the measurement result when the transmittance is medium is indicated by (▲), and the measurement result when the transmittance is high is indicated by (●). is there.
[0058]
As can be seen from this result, when the transmittance is small, the frequency of occurrence of the snow detection distance is highest around 2 m, and it can be said that the scattered light data is generated in a range of 5 m or less. When the transmittance is moderate, the frequency of occurrence of the snow detection distance is highest around 3 m, and it can be said that the scattered light data is generated in a range of 6 m or less. When the transmittance is large, it can be said that the light is generated almost uniformly in the range of about 2 to 7 m as the distance for detecting snow, and the scattered light data is generated in the range of 8 m or less. Therefore, if 8 m is set as the scattered light data, it is possible to sufficiently cope with the case where the transmittance is large as well as the case where the transmittance is small. Although FIG. 5 shows the measurement results for snow, it has been found that fog and rain show almost the same tendency.
[0059]
If the first data is continuously smaller than the scattered light data by a predetermined number of times n (S170: YES), it is determined in S175 that it is in a snow / fog state, and information indicating that the snow / fog state is present. And then returns to S100. When snow and fog are occurring, the possibility that the first data is continuously smaller than the scattered light data a predetermined number of times n times is very high, and for example, in the case of a vehicle running ahead Since there is almost no possibility that the value will decrease continuously n times, the determination is made in this way.
[0060]
If the first data is not smaller than the scattered light data by a predetermined number of times n (S170: NO), it is determined in S180 whether or not there is information on fog determination. This is because if the first data is not smaller than the scattered light data by a predetermined number of times n consecutive times, it is not enough to immediately determine that the data is not snow / mist. For example, if it is determined in the processing of S140 or S175 that the state is snow and fog, and information indicating that the state is snow and fog is stored, it cannot be determined that the state is snow and fog. Since it cannot be determined otherwise, the determination is suspended in S185 and the process returns to S100.
[0061]
On the other hand, if a negative determination is made in S180, that is, if fog determination is not being performed, it may be determined that there is no fog or the like, and the process proceeds to S155 to output first data.
As described above, in the distance measuring device 1 of the present embodiment, the laser light H is emitted intermittently, a plurality of reflected waves are detected for one emitted laser light H, and each reflected wave is The distance can be measured by measuring the time difference. Therefore, as illustrated in FIG. 4, for example, even when there is a fog on the near side and there is a target object whose distance is to be measured originally on the other side, the reflected wave from the fog on the near side and the original The reflected wave from the target whose distance is to be measured can be detected together, the time difference due to the reflected wave from the fog on the near side can be measured, and the time difference due to the reflected wave from the target can be measured without overlooking.
[0062]
And, simply measuring a plurality of distance data cannot determine whether it is due to fog or the like or a target object to be measured, so the physical properties such as fog are taken into account for the determination. . That is, in the case of weather conditions such as snow, fog, and rain, a distance range corresponding to a reflected wave generated by scattering and reflecting a transmission wave by particles floating in the air in advance is stored in advance. Then, when substantially the same short-distance data is present for all the areas being scanned (S135: YES), it is determined that the area is in the snow / fog state, or the scattered light data is compared with the first data. (S160), if the first data is continuously smaller than the scattered light data by a predetermined number of times n (S170: YES), it is determined in S175 that the state is snow / fog.
[0063]
By making such a determination, it is possible to accurately measure the distance to the target object, such as the distance to the preceding vehicle that should be measured.
In S150, it is determined whether or not the own vehicle is running, and the subsequent processing is changed based on the determination result. For example, if a low-reflection object (as described above, a person wearing dark clothes, a dirty car, a dark car, or a lower portion of a truck bed) is at a short distance, “occurs at a short distance”. In addition, it is the same as fog etc. with the characteristic of “small reflectance”, and it is not possible to distinguish between reflected light from a low reflection object or scattered reflected light from fog etc., but taking into account the condition that it is running Is solved.
For example, when the preceding vehicle is traveling at a speed higher than the traveling speed of the own vehicle or when the obstacle is immovable (including a stopped vehicle), the time difference data to the object changes immediately, and Even when the preceding vehicle is running at the same speed as the own vehicle, it is rare that the exact same speed continues, and the distance between both vehicles is constantly changing, and it is constant for a predetermined time or more. Is considered very low.
[0064]
Incidentally, if the distance to the target is measured in this way, various controls such as a control for preventing a rear-end collision based on the measured distance and a following-running control for performing a following-running while maintaining a predetermined inter-vehicle distance with respect to a preceding vehicle. Can be used to control Further, the distance measuring device 1 of the present embodiment can be applied to various uses other than being mounted on an automobile.
[0065]
Further, in the above embodiment, the obstacle is detected by radiating the pulsed laser light H by the semiconductor laser diode 19, but other configurations such as using radio waves, ultrasonic waves, or the like may be used. In this case, the same operation and effect as in the above embodiment can be obtained. Therefore, an appropriate transmission wave according to the purpose of use of the distance measuring device 1 may be selected.
[0066]
Furthermore, the distance measuring device 1 of the present invention is not limited to the above embodiment, and can be configured in various modes without departing from the gist of the present invention. Hereinafter, two examples will be described as other embodiments.
[Another Example 1]
In the above embodiment, when the drive signal from the arithmetic unit 33 is input to the scan mirror 35 via the motor drive unit 49, the mirror 47 swings and scans a predetermined area, so that the laser light H A so-called scanning method in which sweep irradiation is performed at a predetermined angle in front of the camera is adopted. However, the present invention is not limited to the scan method, and can be similarly implemented even with a fixed method.
[0067]
In the case of this fixed system, the scan mirror 35 and the motor drive unit 49 are not required, and the laser beam from the laser diode 39 in a range of a predetermined angle (about the same as the predetermined angle that is swept and irradiated in the case of the scan system) is emitted. It will be irradiated.
The processing in the case of the fixed system will be described with reference to FIG. In the case of the scanning method, it is determined whether or not scanning of all areas has been completed in S110 in FIG. 2, grouping of distance data according to the distance in S125, and all areas being scanned in S135. It has been determined whether or not substantially the same short-distance data is present in many areas in the interior. However, in the case of the fixed system, these processes cannot be performed due to the difference in the system.
[0068]
Instead, when the multi-lap data exists (S220: YES in FIG. 6), the scattered light data is compared with the first data (S225), and the first data is more than the scattered light data by a predetermined number m. If the number is small continuously (S230: YES), it is determined that the first data is due to scattered light from snow and fog (S235), and the second data is output as the distance to the target in S240. It returns to S200.
[0069]
Unless the first data is continuously smaller than the scattered light data by a predetermined number of times m (S230: NO), it is determined that the first data is not due to scattered light from snow or fog or is so. Cannot be determined, the first data is output as the distance to the target in S250, and the process returns to S200.
[0070]
If there is no multi-lap data (S220: NO), the process proceeds to S245 to determine whether or not the vehicle is traveling, and performs processing in accordance with each determination result. Since the processing is the same as the processing of 160 to S185, it will not be described again.
[0071]
In both S225 and S255, the scattered light data and the first data are compared, and in S230, it is determined whether or not the number is small continuously m times, and in S255, it is determined whether or not it is small continuously n times. I have. The number of times m and the number of times n may be set to an appropriate number according to each case, but do not prevent the same number of times.
[Another Example 2]
Next, another embodiment 2 will be described. As a main aspect of the present invention, it is assumed that data due to snow or fog has a specific property, and data reflecting the specific property is distinguished from data based on an original target (that is, not adopted). It is mentioned. Therefore, let's consider properties such as snow and fog in more detail.
[0072]
The time difference data corresponding to the reflected wave generated by scattering and reflection by particles floating in the air under weather conditions such as snow, fog, rain, etc. is mainly due to the so-called light curtain phenomenon by these floating particles In principle, substantially the same time difference data should be obtained. Therefore, in the above-described embodiment, as described in the description of S135 in FIG. 2, the processing is performed on the assumption that particles such as snow and fog are almost uniformly present in the entire area to be scanned.
[0073]
However, it is also conceivable that the density of suspended particles is different within a predetermined angle range during scanning. In particular, in the case of fog, it is sufficiently possible that local fog is generated. Such a difference in the density of the suspended particles is reflected in a difference in transmittance with respect to a laser beam as a transmission wave. That is, if the transmittance is low, the detection signal level of the reflected wave will increase as a result, and its peak value will also increase. Conversely, if the transmittance is large, the detection signal level of the reflected wave becomes small, and the peak value becomes small.
[0074]
FIG. 8A shows, as an example of a schematic image of the detection signal, three detection signal curves L1 to L3 when the transmittance is different. As shown in FIG. 8A, the detection signal is made valid at the time when the detection limit is exceeded, so that the three detection signal curves L1 to L3 have different times when the detection limit is exceeded. Assuming that the times at which the curves L1, L2, L3 exceed the detection limit are respectively t1, t2, t3, a distance corresponding to the time difference occurs as a measurement error. That is, although snow, fog, and the like exist, they may not be detected as substantially the same time difference data due to partial differences in their densities (density of suspended particles).
[0075]
Thus, in the second embodiment, even when such different time difference data is measured, it can be determined that the data is snow, fog, or the like. The processing in the second embodiment will be described with reference to FIG. The processing in FIG. 7 is different from the processing in FIG. 2 only in the processing in S135 in FIG. 2 and the processing in S335 in FIG. That is, the other processes (S300 to S335, S340 to S385) are the same as S100 to S135, S140 to S185 in FIG. 2, respectively, and thus only the process of S335 will be described.
[0076]
In S335, it is determined whether or not there is distance data smaller than the scattered light data in many areas. The scattered light data is, for example, about 8 m as described above. As shown in FIG. 5, in the case of snow or fog, the distance to be detected is within 8 m even when the transmittance is large as well as when the transmittance is large. Even if a state where the transmittance is partially large within the range occurs, if there is distance data smaller than the scattered light data in many areas, it is determined to be snow or fog (S340). Then, in that case, the first data is not used, and in S345, the second data is output as the distance to the target.
[0077]
In the second embodiment, as shown in FIG. 8A, times t1, t2, and t3 at which the three detection signal curves L1 to L3 exceed the detection limit are different, and further correspond to these time differences. The description is based on the premise that the distance becomes a size that cannot be ignored, and is effective in such a case. However, if the component for detecting the reflected wave and converting it into a signal has a function of making the rising of the detection signal steep, as shown in FIG. The time difference between the times t1, t2, and t3 at which L1 to L3 exceed the detection limit is shortened, and the time difference can be regarded as substantially the same time difference data. If the resulting time difference can be made smaller than the time resolution of the time difference measuring means, there is no error due to the difference in transmittance in principle. In this case, even in the process of S135 shown in FIG. 2, it can be accurately determined that the data corresponds to snow / mist.
[0078]
In this manner, the component for detecting and converting the reflected wave into a signal can be regarded as substantially the same time difference data in which the time difference due to the difference in transmittance is short, or the detection signal is configured so that no error occurs. In order to make the rising steep, it is conceivable to reduce the inductance (inductive, capacitive) around the laser diode 39 in the laser light emitting portion. Such a technique has been realized in the field of optical communication and the like, and for example, there is a light emitting half width at about several nsec. In this case, it is necessary to extend the frequency band of the light receiving unit. For example, as the light receiving element 43, an element such as an avalanche photodiode (APD) can be used.
[0079]
Further, if the rising of the detection signal is made steep, the distance measurement accuracy is improved by itself, and the variable gain amplifier 53 and the peak hold circuit 63 do not need to be particularly used, which contributes to simplification of the configuration.
[0080]
【The invention's effect】
As described above in detail, in the distance measuring device of the present invention, a plurality of reflected waves can be detected for one radiated transmission wave, and the time difference corresponding to each reflected wave can be measured. Even if there is a fog and there is a target object whose distance is to be measured on the other side, the target object that measures the time difference due to the reflected wave from the fog on the near side and that should measure the original distance in the distance The time difference due to reflected waves from can be measured without overlooking. Further, in the case of weather conditions such as snow, fog, and rain, the range of the time difference corresponding to the reflected wave generated by the particles floating in the air scattering and reflecting the transmitted wave is stored in advance and measured. The distance to the reflecting object can be calculated based on the time difference and the stored time difference range data in the case of the scattered reflection.
[0081]
Therefore, in the present invention, even if a reflected wave from a fog or the like is detected by detecting reflected waves from a plurality of reflecting objects with respect to the same transmitted wave, distance measurement can be performed when a signal from a target exists. It is.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating a distance measuring device according to an embodiment.
FIG. 2 is a flowchart illustrating a distance measurement process according to the embodiment.
3A and 3B are time charts showing various signals at the time of distance measurement, where FIG. 3A shows a case where there is one reflected signal, and FIG. 3B shows a case where there are two reflected signals.
FIG. 4 is an explanatory diagram showing the concept of distance measurement.
FIG. 5 is a graph showing the relationship between the distance at which snow is detected and the frequency of occurrence thereof.
FIG. 6 is a flowchart illustrating a distance measurement process when laser light is irradiated in a fixed manner as another embodiment 1.
FIG. 7 is a flowchart illustrating a distance measurement process according to another embodiment 2.
FIG. 8 is an explanatory diagram showing a difference in detection signal level and the like when the transmittance is different.
[Explanation of symbols]
1. Distance measuring device 31. Transmitter / receiver
33 arithmetic unit 35 scan mirror
37: Light-emitting lens 39: Laser diode
41: light receiving lens 43: light receiving element
45 ... Drive circuit 47 ... Mirror
49: Motor drive unit 51: STC circuit
53: Variable gain amplifier 55: D / A converter
57: comparator 61: time measurement circuit
63: peak hold circuit H: laser beam

Claims (5)

A time difference measurement unit that intermittently radiates a pulsed transmission wave to detect a reflected wave from a reflecting object, and measures a time difference between a time when the transmission wave is radiated and a time when the reflected wave is detected,
A distance measuring device comprising: a distance calculating unit that calculates a distance to the reflective object based on the time difference measured by the time difference measuring unit.
The time difference measuring means detects a plurality of reflected waves for one radiated transmission wave, and is configured to be able to measure a time difference corresponding to each reflected wave,
In the case of weather conditions such as snow, fog, and rain, storage means for storing in advance the range of the time difference corresponding to the reflected wave generated by scattering and reflecting the transmission wave by particles floating in the air in the case of weather conditions,
The distance calculating means calculates the distance to the reflecting object based on the time difference measured by the time difference measuring means and the time difference range data in the case of scattered reflection stored in the storage means. Distance measuring device. The distance measuring device according to claim 1, which is mounted on a vehicle,
It is provided with traveling determination means for determining whether the vehicle is traveling or not,
The distance calculating means includes, in addition to the time difference measured by the time difference measuring means and the time difference range data in the case of scattered reflection stored in the storage means, whether or not the vehicle is running by the travel determining means . A distance measuring device for calculating a distance to the reflective object based on a result of the determination. The distance measuring device according to claim 2,
When the vehicle is traveling and the time difference measured by the time difference measuring means continuously enters the time difference range of the scattered reflection stored in the storage means for a predetermined number of times or more, the time difference is determined to be fog. A distance measuring device that determines that the distance is due to scattered reflection from the object, and calculates the distance to the reflective object based on other time difference data. The distance measuring device according to claim 1, which is mounted on a vehicle,
The time difference measuring means scans and emits the transmission wave in a predetermined angle range in the vehicle width direction, and is configured to be capable of detecting the time difference corresponding to the scan angle,
When a plurality of reflected waves are detected for one transmission wave, and the time difference corresponding to each reflected wave is measured by the time difference measuring means, the shortest time difference data among the plurality of time difference data is the number of times A determination unit for determining whether or not the scan angles are substantially the same,
If the determining means determines that there is substantially the same shortest time difference data at many scan angles, the distance calculating means determines the next time difference data next to the shortest time difference data among the plurality of time difference data. A distance measuring device that calculates a distance to the reflective object based on the distance. The distance measuring device according to claim 1, which is mounted on a vehicle,
The time difference measuring means scans and emits the transmission wave in a predetermined angle range in the vehicle width direction, and is configured to be capable of detecting the time difference corresponding to the scan angle,
When a plurality of reflected waves are detected for one transmission wave, and the time difference corresponding to each reflected wave is measured by the time difference measuring means, the shortest time difference data among the plurality of time difference data is the number of times At the scan angle, comprising a determination means for determining whether or not within the time difference range in the case of the scattered reflection stored in the storage means,
When the determination means determines that the shortest time difference data is within the time difference range in the case of the scattered reflection at many scan angles, the distance calculation means determines the distance among the plurality of time difference data. A distance measuring device for calculating a distance to the reflective object based on the longest difference data next to the shortest difference data.

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